Gut microbiota-derived tryptophan metabolites alleviate liver injury via AhR/Nrf2 activation in pyrrolizidine alkaloids-induced sinusoidal obstruction syndrome

Artemisia capillaris Thunb. Polysaccharide alleviates cholestatic liver injury through gut microbiota modulation and Nrf2 signaling pathway activation in mice

ETHNOPHARMACOLOGICAL RELEVANCE

According to traditional Chinese medicine (TCM) theory, cholestasis belongs to category of jaundice. Artemisia capillaris Thunb. has been widely used for the treatment of jaundice in TCM. The polysaccharides are the one of main active components of the herb, but its effects on cholestasis remain unclear.

AIM OF THE STUDY

To investigate the protective effect and mechanism of Artemisia capillaris Thunb. polysaccharide (APS) on cholestasis and liver injury.

MATERIALS AND METHODS

The amelioration of APS on cholestasis was evaluated in an alpha-naphthyl isothiocyanate (ANIT)-induced mice model. Then nuclear Nrf2 knockout mice, mass spectrometry, 16s rDNA sequencing, metabolomics, and molecular biotechnology methods were used to elucidate the associated mechanisms of APS against cholestatic liver injury.

RESULTS

Treatment with low and high doses of APS markedly decreased cholestatic liver injury of mice. Mechanistically, APS promoted nuclear translocation of hepatic nuclear factor erythroid 2-related factor (Nrf2), upregulated downstream bile acid (BA) efflux transporters and detoxifying enzymes expression, improved BA homeostasis, and attenuated oxidative liver injury; however, these effects were annulled in Nrf2 knock-out mice. Furthermore, APS ameliorated the microbiota dysbiosis of cholestatic mice and selectively increased short-chain fatty acid (SCFA)-producing bacteria growth. Fecal microbiota transplantation of APS also promoted hepatic Nrf2 activation, increased BA efflux transporters and detoxifying enzymes expression, ameliorated intrahepatic BA accumulation and cholestatic liver injury. Non-targeted metabolomics and in vitro microbiota culture confirmed that APS significantly increased the production of a microbiota-derived SCFA (butyric acid), which is also able to upregulate Nrf2 expression.

CONCLUSIONS

These findings indicate that APS can ameliorate cholestasis by modulating gut microbiota and activating the Nrf2 pathway, representing a novel therapeutic approach for cholestatic liver disease.

Pyrrolizidine Alkaloids-Pros and Cons for Pharmaceutical and Medical Applications

Heterocyclic organic compounds named pyrrolizidine alkaloids (PAs) belong to a group of alkaloids and are synthesized by either plants or microorganisms. Therefore, they are naturally occurring secondary metabolites. They are found in species applied in the pharmaceutical and food industries, thus a thorough knowledge of their pharmacological properties and toxicology to humans is of great importance for their further safe employment. This review is original because it synthesizes knowledge of plant and microbial PAs, which is unusual in the scientific literature. We have focused on the Boraginaceae family, which is unique due to the exceptional richness and diversity of its PAs in plant species. We have also presented the microbial sources of PAs, both from fungi and bacteria. The structure and metabolism of PAs have been discussed. Our main aim was to summarize the effects of PAs on humans, including both negative, toxic ones, mainly concerning hepatotoxicity and carcinogenicity, as well as potentially positive ones for pharmacological and medical applications. We have collected the results of studies on the anticancer activity of PAs from plant and microbial sources (mainly Streptomyces strains) and on the antimicrobial activity of PAs on different strains of microorganisms (bacteria and fungi). Finally, we have suggested potential applications and future perspectives.